In order to improve the gain flatness of erbium doped fibre amplifiers, it is known to raise the temperature of the erbium doped fibre by means of a foil heater, thus limiting the temperature excursion experienced by the erbium doped fibre under varying external thermal environments. Such a foil heater typically consists of an etched conductive track, manufactured to a specified length and corresponding resistance, sandwiched between two layers of a non-electrically conducting material.
FIG. 1 shows views from above and one side and an exploded perspective view of such a known optical amplifier in which a specified length of erbium optical fibre is wound around an aluminium spool 2 clamped within a housing 4 by a clamp 6 with the interposition of a thermal gasket 8 and the foil heater 10. The clamp 6 is held in position by a screw 12, and electrical connections to the foil heater 10 are made by way of a standard PCB connector 14 mounted on a projecting portion 16 of the heater.
In such an arrangement the foil heater 10 is pressed hard against the spool 2 through the interface of the thermal gasket 8 so that, when the foil heater 10 is powered up, the heat produced is transferred to the spool 2 and hence to the erbium optical fibre.
However such foil heaters are relatively costly to produce, and thus are a major limiting factor in preventing cost reductions in the manufacture of the optical amplifiers within which they are incorporated. The mechanical complexity of such heaters means that they are necessarily costly to manufacture and assemble.
It is an object of the present invention to provide an optical amplifier incorporating a heater which can be produced at low cost and in such a manner as to simplify assembly of the amplifier and reduce assembly time.